__________ is the only research method that studies cause and effect variables

Don and Betty were overwhelmed for the first several weeks after they brought little Sally home from the hospital. But in time, Sally seemed to become sleepy, fussy, and hungry at fairly predictable intervals, and her parents fell into step with her

behavioral __________. a) stages b) rhythms c) states d) parameters

The risk of Down syndrome increases sharply, especially after age ______.

A. 30 B. 33 C. 35 D. 40